如何优雅的判断List集合中对象的某个字段是否存在重复值

今天遇到需要判断泛型集合中对象的某个字段是否有重复值，所以特此记录一下方法。

这里我们使用Java8的新特性——Strem流，详细代码如下。

实体类如下：

public class Person {
	private String name;
	private Integer age;
	private String gradle;
	
	public Person() {
		super();
	}
	
	public Person(String name, Integer age, String gradle) {
		super();
		this.name = name;
		this.age = age;
		this.gradle = gradle;
	}
	
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getAge() {
		return age;
	}
	public void setAge(Integer age) {
		this.age = age;
	}
	public String getGradle() {
		return gradle;
	}
	public void setGradle(String gradle) {
		this.gradle = gradle;
	}
	
	@Override
	public String toString() {
		return "Person [name=" + name + ", age=" + age + ", gradle=" + gradle + "]";
	} 
	
}

测试代码如下：

public static void main(String[] args) {
		 Person person1 = new Person("小刘", 24, "男");
        Person person2 = new Person("小贺", 18, "女");
        Person person3 = new Person("小袁", 18, "女");
        Person person4 = new Person("小李", 21, "男");
        Person person5 = new Person("小子", 21, "男");
        List<Person> persons = Arrays.asList(person1, person2, person3, person4,person5);
        // 根据指定属性分组，并统计数量（key：指定属性，value：数量）
        Map<Object, Long> mapGroup = persons.stream().collect(Collectors.groupingBy(person -> person.getAge(), Collectors.counting()));
        System.out.println(mapGroup.toString());
        // 筛选Map中value大于1的key
        Stream<Object> stringStream = mapGroup.entrySet().stream().filter(entry -> entry.getValue() > 1).map(entry -> entry.getKey());
        System.out.print("重复的数据：{ ");
        stringStream.forEach(str -> {
            System.out.print(str + " ");
        });
        System.out.println("}");
	}

运行结果如图所示：